The invention relates to a device for regulating the current passing through a self-inductive element, for example a control solenoid of an electromagnetic valve, and including a series branch featuring the said self-inductive element and a control device driven by a control signal so as to supply the self-inductive element from an electrical power-supply source, especially a voltage source, as well as a measuring device supplying a signal for measuring an average current through the self-inductive element, as well as a regulating device for generating the control signal as a function of a datum value and of the measurement signal.
In the regulating devices of known type, the current which passes through the solenoid is determined on the basis of a low-value resistor or shunt inserted in series with the solenoid. The voltage developed by this shunt is then amplified and averaged in a differential amplifier.
Such a device exhibits several drawbacks.
A first drawback is a voltage drop in the control circuit.
A second drawback is that, with the potential difference present at the terminals of the shunt necessarily having to be small, it has to be amplified, and the presence of the amplifier induces an inaccuracy due to the various bias resistors and to the tolerances inherent in integrated circuits.
The U.S. Pat. No. 4,511,829 proposes to take the measurement by the use of a resistor in series with a diode in reverse mode, in parallel with the self-inductive element.
The object of the present invention is to enhance the abovementioned device.
To that end, the invention relates to a device for regulating the current passing through a self-inductive element, including a series branch including the said self-inductive element and a control device driven by a control signal so as to power the self-inductive element from an electrical power-supply source, as well as a measuring device supplying a signal for measuring a current through the self-inductive element and including a device for acquisition of a signal representative of a current through the self-inductive element and a regulating device for generating the control signal as a function of a datum value and of the measurement signal, the acquisition device including, in parallel with the self-inductive element (S), a branch including, in series, a first resistive element (Rs) and a diode (D), the diode (D) being in reverse mode when the control device (PT) is in a state in which the self-inductive element (S) is coupled to the said power-supply source, characterized in that it includes a circuit for averaging the said signal representative of a current in order to produce a signal representative of the average current in the self-inductive element, and in that the averaging circuit includes a transistor (T2) the gate electrode of which receives a switching signal in order to switch the said transistor in opposition with the said control device (PT), the drain electrode of which receives a signal representative of the voltage at the terminals of the said first resistive element (Rs), and the source electrode of which, which constitutes an output of a signal (Vm) representative of the said average current (Im), is connected to a capacitive element (Cm) in parallel with a second resistive element (Rm).
The averaging circuit may also include a transistor, the gate electrode of which receives a switching signal in order to switch over the said transistor in opposition with the said control device, the drain electrode of which receives a signal representative of the voltage at the terminals of the said first resistive element, and the source electrode of which, which constitutes an output for a signal representative of the said average current, is connected to a capacitive element in parallel with a second resistive element.
The drain electrode of the transistor may be connected to the common terminal between the first resistor and the diode via a divider bridge. This divider bridge may have a first end connected to the said common terminal, a second end connected to a voltage source, and a midpoint connected to the said drain electrode, the voltage of the said voltage source being chosen in such a way that the voltage at the said midpoint of the divider bridge has a positive or zero value.